1. Statement of the Technical Field
The disclosed invention is in the field of medical devices and procedures. In particular, the disclosed invention pertains to a novel surgical device and its use for ablation of tissues associated with solid anatomical surfaces such as joints.
2. Description of the Related Art
Lower back pain (LBP) is a common musculoskeletal complaint of industrialized society with a reported 60–90% of the population experiencing at least one episode of LPB per lifetime. As such, LBP is a very common cause of disability in persons younger than 45 years, the second leading reason for visits to primary care physicians, and the most frequent cause of visits to orthopedic surgeons and neurosurgeons. As the most frequently reported work-related injury, LBP is the most costly of all medical diagnoses when the costs of time lost at work, long-term disability and medical and legal expenses are factored in. Over the past century, various structures associated with the spine and back muscles, including the dorsal root ganglia, dura, muscles of the lumbar spine and the facet joints, have been implicated as the source of chronic LBP. Many recent clinical studies implicate facet joints of the spine as the source of pain in LBP. The spine is composed of a series of functional units, each consisting of an anterior segment made up of two adjacent vertebral bodies and the intervertebral disc between them, and the posterior segment consisting of the laminae and their processes. Bones of the spine articulate anteriorly by intervertebral discs and posteriorly by paired joints. The paired joints, known as the facet or zygapophyseal joints, are formed by the articulation of the processes on the laminae of adjacent vertebrae. Thus the superior articular process of one vertebra articulates with the inferior articular process of the vertebra below to form the facet joint.
Facet joints are true synovial joints with a joint space, hyaline cartilage surfaces, a synovial lining, and a fibrous capsule. Nociceptive (pain-sensing) nerve fibers and autonomic nerves have been identified in the lumbar facet joint capsule and synovial folds in recent studies. Inflammation, injury, nerve entrapment and degenerative osteoarthritic changes in the joint tissues all can lead to pain originating in the facet joints. Facet joint pain may also arise secondary to vertebral disc degeneration, owing to facet joint osteoarthritis that develops in response to the primary disc degeneration.
Pain cannot be felt if the nerve pathways that relay pain impulses to the brain are interrupted. Painful stimuli from the facet joints are carried by the medial branches of the dorsal primary rami. On the theory that facet joint-mediated LBP should not be perceived in absence of intact medial nerve pathways, denervation (neurotomy) of the dorsal medial nerve branch has been advocated for treatment of lumbar facet joint pain. Early methods included destruction of the nerves by injection of neurolysing agents; however in recent years radiofrequency (RF) ablation of these nerves is the most widely used technique for denervation of the facet joints.
The target of a needle used for facet joint nerve ablation in the lumbar region (L1–L4 levels) is the portion of the nerve on the dorsal surface of the transverse process just caudal to the most medial end of the superior edge of the transverse process. The approximate vicinity of the target nerves can be determined using fluoroscopic techniques in subjects lying prone on a fluoroscopy table. Specifically, in the RF ablation procedure, under radiographic guidance, an introducer cannula is positioned in the vicinity of the dorsal medial nerve. Ideally the cannula is positioned alongside the nerve, rather than with its point facing the nerve. Once the position of the cannula appears to be correct, based on the radiographic image and the “feel” of the target tissue, the surgeon introduces an RF electrode via the cannula, with the aim of positioning the electrode alongside the nerve. Following positive stimulation at low voltage that reproduces the subject's pain, an RF lesion is created by passing current through the electrode that raises the tissue temperature to 60–80 degrees centrigrade for 60–90 seconds. This portion of the procedure is quite uncomfortable and calls for judicious use of sedation and analgesics.
Existing devices such as RF probes used for denervation of facet joints are placed by surgeons using radiographic techniques (C-arm fluoroscopy) without the benefit of endoscopic guidance to ensure accurate positioning of the electrodes. In fact, proper placement of the needle tip in the complicated structure of a subject's spine requires great skill by the treating clinician. The needles may need to be withdrawn and re-inserted multiple times. Errors in needle placement can result in accidental impalement of structures such as the nerve root in the lower spine, presenting a serious medical risk to the subject.
The success of RF denervation procedures varies widely, with a lower end of 9%. Despite improvements in technological approaches and controls incorporated into later clinical assessments of the efficacy of facet joint denervation as a therapy for LBP, there continues to be a wide range of reported success rates. This wide variability in the procedure in the hands of different practitioners suggests unpredictability inherent in the procedure itself. The unpredictability may be a reflection of failure of existing methods to enable sufficiently precise localization of the target nerve prior to lesioning, combined with incomplete destruction of the pain-causing nerve fibers by the RF electrode.